As it happens, I really couldn't care less how much vis my magus starts out the saga with. We'll have a solid vis salary and I'll have Philosophic Alchemy, so I should have enough moving forward.
What I really do care about is how much vis my magus has to work with during development. My current plan is to go heavily into magic items to deal with the Dominion Aura, including some invested items (particularly a talisman). The idea is a magus with relatively few spells known, but a passel of magic items to make up for the missing spells. Of course that ends up taking a lot of vis compared with a conventional magus who learns spells, since you have to pay vis for magic items whereas spells are free. Moreover, you have to open an invested item with a full compliment of vis, even if you don't fill it up until later. (This is exacerbated by the ability of a Hermetic Alchemist to open up an invested item with more vis than usual. Toss in a familiar and a longevity ritual and the vis they cost and things can get pretty expensive. (more than 75 vis.)
In fact, that was one of the reasons that I decided on the Philosophic Alchemy build, to be able to afford to make a lot of magic items instead of learning a lot of spells. I suspect that silveroak, playing a Verditius magus, is in somewhat the same boat. I'm guessing part of the reason he took a PVS was to be able to afford to make items - though as a Verditius he can make invested items more cheaply, an option I don't have. I have to pay full freight for every invested item meaning that even if he and I started off with the exact same invested items, I'd have paid vastly more vis to create my versions. The end result is that my character is a bit of a vis hog (specially compared to a Verditius magus). But I thought that was okay because I have a magus who is supposed to be able to generate large amounts of vis.
Now, I'm perfectly happy to start out with only a moderate amount of vis at game start, saying that he spent most of it on gifts, bribes, healings, or whatever. I can understand that starting out with too much vis could be unbalancing. But I want to know whether I'll have enough vis to make the items I'm interested in making. Going strictly by the rules, the character could easily have made more than enough vis to account for even the most ambitious magic item building plan. But I'm frankly not certain whether even 75 vis would cover a modest magi item building plan, not when you include a familiar and a longevity ritual.
Furthermore, there's the issue of how long it takes to accumulate a quantity of vis. One of the reasons I was looking at a per year amount was to account for differing hermetic ages. 25 vis accumulated over the course of 5 years is a lot. 25 vis accumulated over 25 years is a paltry amount. I haven't settled on a hermetic age yet, but it seems like our hermetic ages are ranging from 20-50 years so far (not counting your character), a pretty big gap. It just seemed to me that saying all magi have the same vis to work with during development puts the older magi at a huge disadvantage.
That having been said, I can see the desire to fall back on BP for play balance reasons. Maybe a fair compromise is to say that silveroak and I each start off with a lump sum payment for our respective virtues (25 and 75, as you suggest, or whatever number we decide is fair), and any excess we need is paid for out of the BPs we have. It means that my character has frittered away a staggering amount of vis, but I'm willing to accept that.
In the end, I just want to be certain that my magus has enough vis to make the magic items I'd hoped to make. Looking at the character build, he ought to have no problem. I don't want to seem greedy, but with a major and a minor virtue devoted to vis collection, the character should have the vis he needs.